There is evidence which suggests that neural pathways originating from suprapontile areas of the brain and associated with central command signals for locomotion are important in the cardiopulmonary response to exercise. In general, the circulatory and respiratory responses to exercise are not studied in a detailed and integrated manner. The cardiovascular response is comprised of an increased cardiac output and a redistribution of blood flow to exercising muscle. The ventilatory response comprises a coordinated activation of the various respiratory muscles, including the diaphragm, intercostal muscles, muscles of the larynx and upper airway muscles. The precise pattern of the overall cardiopulmonary response can be behavior specific. Little is known concerning the organization of central descending neural pathways which are important in the cardiopulmonary response to exercise. This proposal would examine these issues by comparing the overall pattern of the cardiopulmonary response to spontaneous locomotion, "fictive" locomotion and locomotion induced by stimulation of either the subthalmic or mesencephalic locomotor regions in unanesthetized cats with high decerebrations (thalmic cats). Variables to be measured include heart rate, arterial blood pressure, regional blood flow, left ventricular dP/dt, EMG from the diaphragm, internal and external intercostal muscles, posterior cricoarytenoid muscle of the larynx and the genioglossus muscle of the tongue. This project will provide new information concerning the role of central neural pathways in the cardiopulmonary response to exercise. Also, new and important insights into the central organization of the cardiovascular and respiratory control systems will be obtained as well as the influence of higher brain centers on the cardiopulmonary control systems.